


Backseat Heat

by VampAmber



Series: SPN ABO Bingo: Round Three [5]
Category: Supernatural
Genre: Alpha Castiel (Supernatural), Alpha Castiel/Omega Dean Winchester, Alpha/Beta/Omega Dynamics, Car Sex, Complete, Dean Winchester Has a Crush on Castiel, First Time, John Winchester's A+ Parenting, M/M, Mating Cycles/In Heat, Omega Dean, One Shot, Porn With Plot, SPN A/B/O Bingo, Sam Winchester Needs Brain Bleach, Scents & Smells, Season/Series 05, Smut, Unexpected Heat, Virgin Castiel
Language: English
Status: Completed
Published: 2018-09-10
Updated: 2018-09-10
Packaged: 2019-07-10 19:29:55
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,945
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15955991
Author URL: https://archiveofourown.org/users/VampAmber/pseuds/VampAmber
Summary: When's the worst time for your heat to hit unexpectedly? Dean finds out that it's in the middle of the woods while on a hunt, with Castiel, angel of the lord, a few steps ahead of him. Castiel, who is not only completely alpha, but also so out of Dean's reach that it's not even funny. But maybe Dean isn't as correct about the situation as he thought. And the Impalaisonly a short walk from where they are...





	Backseat Heat

**Author's Note:**

> I'm on a roll, comparatively. Yays! Anyway, this was supposed to just be pure smut, but I accidentally wrote plot. My apologies. Hopefully it's good anyway.
> 
> For this fic, I used the square **Heat/Rut**.

“Son of a bitch.” The words were out of Dean’s mouth before he even thought of trying to keep this new development a secret. And of course, Sam had decided to go off on his own while Cas went with Dean during this part of the freaking hunt. Of course.

If it had just been him and Sam, Dean would have dealt with the teasing, threw back some insults of his own, and then went back to the motel room to whimper for a while and curse his own stupidity for forgetting something this freaking major. But since he was with Cas…

“Dean, is something wrong?” The angel in question asked from a few yards farther down the path.

Dean panicked and went for the worst plan possible. He completely denied everything. “Naw, I just, uhh… touched something gross, is all.” It was bad enough that Dean was embarrassed about being an omega, especially around anybody even half as bad assed as Castiel, angel of the lord and kicker of serious monster butt. It was just too much right now to admit that not only was he a weak omega just like John always said, but he was a dumb one that completely forgot his heat was coming up. His dad would’ve kicked his butt for this, if he’d still been alive. And unlike the situation, there was no denying those twinges in his stomach. Any minute now, every alpha in a three mile radius would probably be able to smell him just by the heavy scent of slick. Every alpha including Cas. Son of a bitch.

“Okay,” Cas replied, trusting Dean because he had yet to learn Dean’s obvious tells. Like how his voice sometimes got slightly higher pitched when he was trying to hide any kind of extreme panic. Monsters were one thing, but embarrassment was a big time red alert for the hunter. “Just let me know if you spot anything.”

Dean winced as the twinges started to turn into actual cramps, and he mentally crossed his fingers that they’d find whatever it was that was killing the campers in this area before he lost too much control. But, as usual, the universe was not on his side. He felt the throbbing start right as he noticed that his boxers weren’t as dry as he’d prefer. He stifled the combination groan/moan as best he could, but damn that angelic hearing.

“Dean,” Cas demanded, abruptly turning around at the unusual sounds coming from the human he’d only known for a short time so far. “Something is obviously wrong, so tell me so that we can finish this hunt.” The angel wasn’t sure why, but he’d been feeling weirder and weirder as they searched. There was something in the air…

“It’s nothing,” Dean grunted, still trying in vain for full denial of the situation.

“No, it’s not,” Cas scolded him. His blood pressure was raising, but still, he wasn’t sure of the cause. He’d thought angels knew all about their Father’s creatures, including monsters, but he didn’t know of any to cause such effects. “Tell me,” he said, almost growling. Instincts he hadn’t known he had were starting to flare up. He’d never been in a human vessel for this long, so confusion was only natural, but this was a bit much, even for him.

“Nothing,” Dean mumbled, before doubling over in what Cas could only assume was pain.

“You’re hurt!” Cas rushed towards the hunter, and was hit with a smell he’d never before encountered. It was new, but it was also the most amazing thing the angel had even sensed. “Dean?”

“It’s my heat,” Dean whispered, and another delicious wave of heavenly scent wafted towards Cas.

The angel knew of the dynamics of the humans, of alphas and omegas and heat cycles, but he’d never experienced it before. He knew that, when inside this vessel, he was an alpha, and that Dean was an omega, but everything he knew was theory only. The sweet scent that was starting to drive his instincts mad, now that he knew at least some of what was going on, could only be what they called ‘slick’. But why Cas was reacting the way he was, he had no idea.

“Shit, Cas, I need… I need to get back,” Dean pleaded. “Hotel room, I need…” The hunter was beyond embarrassed to be begging Cas for anything like this, but he knew that there was a toy in his bag and some pills that would make him feel a little less unstable. Dildos were as unsatisfying as it got, but it was better than going out and slutting himself up to some random alpha. “Please?” There went any hint of self respect.

Cas just tilted his head, deep in thought. He was remembering more about the dynamics, specifically the heat cycle. He knew that an omega needed an alpha to make them feel better, because this was the humans’ primitive way of ensuring the propagation of the species. It all boiled down to breeding. Dean’s body wanted to be bred. A child rarely resulted from an angel and human coupling, and Cas could sense something running through Dean’s subconscious about ‘birth control’, so he decided to offer his assistance. “I could help you,” he stated.

“Son of a bitch!” Dean shouted in annoyance. “Cas, I don’t care who you are, I’m not taking a damn pity fuck from you,” he ground out, his rage momentarily blocking out his hormones. “Just because I’m a weak-ass omega doesn’t mean I put my ass in the air for any alpha hoping for a quick knot. I’ll just drive myself back to the motel, if that’s how you’re going to be.” He whirled around and angrily marched off towards the parking area, which thankfully wasn’t too terribly far off.

“Dean!” Cas called after him, and with a ruffled feather noise, the angel was standing in front of the omega. “I didn’t mean it that way,” he tried to explain. His instincts, his hormones, everything was going haywire in his head. When other angels had taken hosts for long periods, they’d never talked about anything like this. But then again, Cas remembered, none of them had ever had the vessel all to themselves, without a human soul off to the side. It hadn’t been that long since Raphael had blasted him, sending Jimmy Novak safely to Heaven.

“Then how did you mean it, _alpha_?” Dean asked, making the designation sound like an insult.

Pieces were starting to click into place in the angel’s head. Maybe now that he was the only one in this body, he was subject to all the human instincts and urges? Especially those that led to mating. The more Cas stood this close to Dean, the more his body reacted. He’d not dealt with sexual urges before, but from watching humans he knew enough about them to know what the stiffening of the penis in a male meant. And the more he thought about it, the more he realized he’d felt like this towards Dean before, only not to such an extent. He… appreciated the omega more than anyone else. Was willing to do things for Dean that he wouldn’t do for even Sam, though they were both technically his friends. Cas was… attracted to the omega. That was the best term for it. Attracted. And right now, what he really wanted to do was mate with Dean and feed the attraction even further.

“I want to help you, Dean,” Cas started, figuring it all out as he went. “I want it to be me that helps you. No one else.”

Dean’s eyes widened, and his scent intensified. “Are you saying what I think you’re saying?” He asked, praying that the answer was yes, completely forgetting that angels heard prayers. Yeah, maybe a little crush had been forming on the weird, goofy angel, way back in the back of the omega’s brain. That night in the barn, even though it had been pretty damn terrifying at the time, had been really hot in retrospect. And Dean had to admit that the angel had only gotten hotter as the weeks and months went on. Okay, maybe crush was putting it lightly. Dean didn’t do the ‘L’ word, but maybe that’s what it was turning into?

“I think,” Cas said slowly, “that I want you.” He licked his lips nervously, making Dean let out a tiny, microscopic whimper as his pants grew damper. “I think I… have wanted you. For a while.”

“Just think?” Dean said, only partially teasing. Apparently emotional drama and major angst was enough to shut up his heat for a few minutes. Any soap opera would be proud.

“It’s…” Cas fumbled over his words. “I haven’t dealt with anything like this before,” he tried to explain. “Before, the human parts were more separate. I didn’t have to deal with them.”

“Yeah?” Dean thought he was following Cas right.

“But now, without Jimmy, I’m… I’m dealing with them. And it’s confusing, but I at least know that I feel something towards you, Dean. Something in me is drawn to you.”

Dean’s hopes dropped painfully. “Yeah, drawn to me like every other alpha right now, with me radiating ‘fuck me, fuck me’ like a pro.”

“No Dean, I was always drawn to you. It’s just harder to deny right now,” Cas responded, giving Dean a pleading look, begging to be understood. At least Dean didn’t have to be alone in the pathetic department now.

“So it’s not just a heat thing?” Dean asked, just to make sure. Said heat was tired of the melodrama by now, and the twinges and cramps were needling their way back in at full speed.

“No, Dean,” Cas confirmed.

Dean stared at the angel for a few moments, not sure he could believe what he was hearing. But when his lust meter went from sane to through the freaking roof, he knew that right now there was only one good option. He never would’ve made it to the motel room anyway. “Cas, car, now,” Dean said, grabbing Cas’ collar and dragging him in the direction of the Impala. Hopefully they could at least make it that far.

The sound of rustling feathers and a wave of vertigo that would knock a moose to the floor signaled to Dean, before he could make out shapes again, that Cas had teleported them to Baby. “You need to quit doing that without warning,” Dean grumbled as he dug the car keys from his pocket, the powerful need of his heat the only thing keeping him from succumbing to the dizziness.

“My apologies,” Cas said, fidgeting in a way that mirrored how Dean felt on the inside right now.

“Hop in,” Dean instructed, once he had Baby’s backseat door wide open.

Cas stared in confusion. “I’m not sure how…” He trailed off, tilting his head in that way that made Dean want to kiss him. So the omega grabbed him by the collar again and did. The angel was obviously completely inexperienced, but damn was he a quick learner. Their mouths worked on devouring each other as slick started to drip down Dean’s legs.

“Lay down and get naked,” Dean whispered into Cas’ ear as they drew apart. He started to take his own clothes off so he’d be ready as well, and then a different kind of fluttering sound happened, and Dean was buck naked, standing next to his car in the middle of the woods, staring down at an equally naked angel in the backseat. “I am really liking those superpowers,” he said with a smirk as he started to climb in after Cas. Then his heat knocked him metaphorically sideways, and the time for joking was over.

“Dean,” Cas growled, pulling him down for another kiss as soon as he was close enough. The alpha’s erection pushed again Dean’s stomach reminding him of how big it had looked from the outside. Dean let out moan after moan as he and Cas kissed, desperately grinding against each other.

In the back of Dean’s mind, so far back he didn’t even catch it, was a worry that he’d have to redo the backseat after this because of the sheer amount of slick that was pulsing out of him, but since it was so far back, Dean couldn’t care less about it right now. Instead, he was focused on the alpha underneath him, the one that smelled better than even the best burger and beer with pie for dessert. “Fuck, Cas,” he moaned. “Need you in me now.”

“I don’t… I’m not sure…” Cas stuttered, and looked like this was the worst thing that had ever happened to him. Seeing as how they were mid-apocalypse, that was really saying something.

“Here,” Dean muttered as he grabbed Cas’ dick to maneuver it correctly. It had been awhile since he’d had sex in the backseat of a car, but those skills never got rusty, as far as Dean was concerned. He let out the raunchiest damn groan as he felt Cas slide in, his hole so wet and desperate that he didn’t even need time to adjust before taking it all. If he thought it had looked big, having it push inside him made it seem impossibly huge. And impossibly perfect. “Now move,” he said as he started to move in example. When Cas gave him a confused look, Dean rolled his eyes. “At least you’re pretty,” he joked. “Just do what your instincts say to.” Apparently, that was the exact right advice to give, because soon Cas was thrusting into Dean, making him writhe and moan like a porn star. Sex had never felt even half this good before.

“Dean, yes,” Cas panted out, pushing even harder. “Need you, Dean.” Dean sloppily crashed his mouth onto Cas’, and their moans and sighs were happily swallowed up as they both grinded with all they had.

“Harder!” Dean screamed, so close already. Cas obliged, and Dean’s mind exploded as his orgasm blew over him like a freaking hurricane. “Holy fuck yes, Cas!” He wailed, feeling his come coat both their chests as he moved in ecstasy, slick probably ruining the seat leather by now.

Cas’ rhythm started to falter, and Dean felt as his knot catch, giving the omega a second, lesser orgasm as he felt the angel spilling his load inside him. Cas was glowing by now, quite literally. Dean stared in awe as the angel had what was most likely his first orgasm. Dean was completely ruined for regular sex now.

“That was… amazing,” Cas said, out of breath as the glow slowly faded.

“You were amazing,” Dean said into Cas’ neck as he started to nuzzle up to the alpha. He’d never been much for the cuddling part of sex, even with a knot tying him there. But something about Cas made him want to rub up against him, purring like a lovesick kitten. The omega let out a happy sigh as Cas started to run his hand through Dean’s hair.

“Dean,” Cas started to say, in a voice serious enough to take away most of Dean’s figurative afterglow. “I’m not sure what exactly I’m feeling, not in human terms at least,” he explained. Dean held his breath, waiting for the inevitable bad news. “But I do know that this feeling, being with you, like this, or any other way, it’s what I want. I want to… not keep you, that doesn’t sound right. But it’s basically what I want.”

Dean let his held breath out, relieved beyond measure. “It kinda sounds like mating,” he said hesitantly.

“Mating would be staying like this always, right?”

Dean smiled, starting to think that ‘L’ word would be coming a lot sooner than expected. “We wouldn’t always be having sex, but otherwise, yeah, that’s what mating is like.”

Cas smiled, an expression Dean had never seen on the angel before, with the grin so big his gums showed. “Then yes, I would like that.”

It was almost too much, but he wasn’t even close to being stupid enough to not grab this chance and hold it as tight as possible. “I’d like it too, Cas.” Completely content, he snuggled up to Cas as close as possible, and dozed with a happy smile on his face, the kind most hunters don’t have the luxury of ever using.

He was woken abruptly at the yelled words “Oh my god, Dean, gross!” Dean opened his eyes and looked up to see his brother standing next to Baby, his face looking like he was about to hurl. “I did not need to see this!” Sam yelled again, not even bothering to be polite. “I come back for flashlight batteries, and now I have to buy brain bleach,” Sam muttered to himself as Dean chuckled.

“My heat hit,” Dean said, his face still looking highly amused. “Cas helped, and if you don’t want to see us naked and covered in porn levels of bodily fluids, I suggest you look away now.” Without waiting for a response, Dean pushed himself off of Cas and winked at his… mate? Cas winked back, and that fluttering noise sounded before they were both dressed, as well as clean. Even the seat was clean, a fact that not-currently-having-sex Dean could appreciate. “Thanks,” he said to Cas before giving him a quick kiss.

“We’re riding with the windows down when we head back, and no way in hell am I sitting in the backseat,” Sam demanded. Dean looked at Cas, and even though it wasn’t funny, they both burst out laughing.

**Author's Note:**

> Just in case anybody was wondering, I'll be at IndyCon in a few weeks. I even have a crazy!Cas cosplay I'm gonna wear on Saturday. Hopefully, I'll be the only crazy!Cas wearing a unicorn horn (cuz I'll be Meg's unicorn, get it?). Not that anybody cares, but if you see me, say hi if you want. I still find it hard to believe that people actually read and like my stories. ^_^


End file.
